Mapping Question

[SiClops]

So I take a 7.5 minute topo map and a lat/log ruler and try to figure out the coordinates for a place. I calculate:

N 47º 31' 58" W 121º 49' 38"

(Messed up and got a map with lat/lon instead of UTM )

 

My trusty little yellow GPSr shows:

 

N 47º 31' 42.5" W 121º 49' 31.8"

 

So how did I do? Is that much error considered really good, ok. or go back to map school? just wondering if I have it figured out or not.

 

Si

[+CO Admin]

So I take a 7.5 minute topo map and a lat/log ruler and try to figure out the coordinates for a place.  I calculate:

N 47º 31' 58"  W 121º 49' 38"

(Messed up and got a map with lat/lon instead of UTM  )

 

My trusty little yellow GPSr shows:

 

N 47º 31' 42.5"  W 121º 49' 31.8"

 

So how did I do?  Is that much error considered really good,  ok. or go back to map school?  just wondering if I have it figured out or not.

 

Si

You need to make sure that both the map and the GPS are using the same Datum.

Chances are the Map is CONUS NAD 27 and the GPS is set for WGS 84.

 

that can make a big difference.

Edited August 12, 2004 by CO Admin

[Tahosa and Sons]

Purchase Nat. Geo's TOPO and make your own maps, and you set the datums to the same as the GPS. Then learn how to use UTM's to measure position and distances.

[+fizzymagic]

Or use ExpertGPS, which gets the topo maps from the Internet and calibrates them for you. Useful with other kinds of maps, too.